1. Field of the Disclosure
The embodiments herein generally relate to wireless communications. More particularly, related to a mechanism of managing indication of Coverage Extension (CE) level between a Bandwidth reduced Low complexity User Equipment (BL UE) and a base station (eNB).
2. Description of the Related Art
Machine-type communication (MTC)/Machine to Machine (M2M) communication is advancing rapidly. The MTC communication facilitates a direct communication (requiring seldom human-machine interaction) with one or more Bandwidth reduced Low complexity (BL) User Equipment(s) (UEs) deployed therein. The BL UEs (i.e., MTC/M2M devices such as Internet of Things (IoT) device(s), wireless transmit/receive units (WTRUs)) are based on 3GPP/Long Term Evolution (LTE) based protocols, with intention of saving power and reduce congestion in a network.
The 3GPP in release 13 is working on further enhancements to a physical layer (PHY) for the BL UEs which is a cellular solution towards the MTC/M2M devices. The 3GPP is working towards using the LTE as a competitive Radio Access Technology (RAT) for efficient support of the MTC. It is envisaged that BL UEs can be deployed in huge numbers, large enough to create an eco-system on its own. Lowering the cost of the BL UEs is an important enabler for implementation of the MTC/M2M devices in the eco-system. It is expected that the BL UEs can communicate to the network with infrequent small burst transmissions.
These BL UEs are expected to require low operational power consumption and hence will have limitations and restriction for following several LTE procedures. For example the LTE supports system bandwidth of up to 20 MHz per carrier and each BL UE may include two antennas and two receive RF chains. It is the 3GPP requirement that the BL UEs operates only in a limited bandwidth of 1.4 MHz. This bandwidth restriction is applicable to the downlink (DL) and uplink (UL) transmissions, the RF baseband components, the data and control channels. However, each of the BL UE should be able to hop across the entire system bandwidth with the operational bandwidth of 1.4 MHz.
The 1.4 MHz on which the BL UEs operates is termed as MTC sub-band. In order to reduce the cost of the BL UEs it is also a requirement that each of the BL UE to possess a single receive RF chain. The peak data rate of BL UEs is also restricted and the reduced operational bandwidth is one of the factors resulting in this. The maximum transport block (TB) size is not expected to be greater than 1000 bits.
In addition to cost reduction, the BL UEs can also support operation under extended coverage (i.e., Coverage Extension (CE)). This CE is achieved by performing repeated transmissions of the same message. These repetitions may be of same or different Hybrid Automatic Repeat Request (HARQ) redundancy versions (RV). There are 4 distinct CE levels including normal coverage, which will be supported by the BL UEs supporting operation under the CE mode. Each CE level is associated with a fixed number of transmission repetitions to achieve the extended coverage.
Further, for the UL transmission, as each of the BL UE by itself can calculate its serving CE level, the number of repeated versions of transmissions required is known to the BL UE. However, for an eNodeB (eNB) to send any message to the BL UE, the CE level currently serving the BL UE has to be known. Based on the knowledge of CE level, the network can then apply the number of repetitions to the message for transmission. In RRC connected state, network receives the UL transmission from the BL UE based on which the network can be able to determine the CE level of BL UE and perform the corresponding number of repeated transmissions.
In RRC idle state, as there is no UL transmission to the network based on which the network could determine the CE level for the BL UE. In order to send a paging message to the BL UE, the network needs to know the CE level of the BL UE. Therefore, it is important that the network is aware of the CE level required by the BL UE. Therefore, new procedures to determine the CE level of the BL UE and to indicate the same to the network have to be introduced.
Furthermore, in the existing LTE system, only one paging message is transmitted over one default paging cycle. There are no repetitions/retransmissions of the paging message that eNB transmit over the same paging cycle. As provisioned in the current 3GPP specifications, during idle state Discontinuous Reception (DRX) the BL UE will wake up during its calculated PF (Paging Frame) and monitor PO (Paging Occasion). PO is monitored at most once and then the BL UE moves back to the DRX sleep state. The PO and PF is calculated as shown below:SFN mod T=(T div N)*(UE_ID mod N)i_s=floor(UE_ID/N)mod Ns
TABLE 1PO for FDD/Frame structure type 1PO whenPO whenPO whenPO whenNsi_s = 0i_s = 1i_s = 2i_s = 319N/AN/AN/A249N/AN/A40459
TABLE 2PO for TDD/Frame structure type 2PO whenPO whenPO whenPO whenNsi_s = 0i_s = 1i_s = 2i_s = 310N/AN/AN/A205N/AN/A40156
In order to accommodate for the BL UE for which multiple repetitions of paging message are to be received, the existing mechanism of paging reception is not optimal and certain optimizations are required. The optimizations for enhancing the efficiency of paging message transmission by eNB and reception by the BL UE are required.
The Random Access Channel (RACH) procedure in the LTE is a four step process where a preamble signature is transmitted to the network as MSG1. Following successful reception of the preamble by the eNB, MSG2/Random Access Response (RAR) is transmitted by the eNB 104. The RAR contains the preamble ID to which the RAR is associated and UL grants for transmitting MSG3. On successful reception of the MSG3, the network sends MSG4 which indicates the completion of the RACH procedure.
The LTE supports two Random Access (RA) preamble groups which are differentiated based on the size of the UL message to be transmitted in the MSG3 during the RACH procedure. There are multiple RA preamble formats (0-3 in case of FDD and 0-4 for TDD) in the LTE which differ in length of the sequence and its corresponding cyclic prefix. The preamble format to be used is signaled by the network over System Information (SIB's). Based on these and other parameters signaled by the network, a UE selects a preamble and transmits it to the eNB over a Physical Random Access Channel (PRACH). In order for the eNB to send RAR to the UE, the eNB shall be educated if the UE is the BL UE and the CE level required by the BL UE. Therefore, new mechanisms to signal CE level to the eNB during PRACH are required.
Mobility procedures for the BL UE are different from that of other UEs (i.e., other than the BL UE's); as the BL UEs operate in a restricted bandwidth of 1.4 MHz which the other UEs on the same cell operate on the LTE system bandwidth which may be as high as the 20 MHz. Therefore, enhancements to these mobility procedures are required.